Extending the Capabilities of Single Particle Mass Spectrometry: II. Measurements of Aerosol Particle Density without DMA

Particle density is an important and useful property that is difficult to measure because it usually requires two separate instruments to measure two particle attributes. As density measurements are often performed on size-classified particles, they are hampered by low particle numbers, and hence poor temporal resolution. We present here a new method for measuring particle densities using our single particle mass spectrometer, SPLAT. This method takes advantage of the fact that the detection efficiency in our single particle mass spectrometer drops off very rapidly as the particle size decreases below 100 nm creating a distinct sharp feature on the small particle side of the vacuum aerodynamic size distribution. Thus, the two quantities needed to determine particle density, the particle diameter and vacuum aerodynamic diameter, are known. We first test this method on particles of known compositions and densities to find that the densities it yields are accurate. We then apply the method to obtain the densities of particles that were characterized during instrument field deployments. We illustrate how the method can also be used to measure the density of chemically resolved particles. In addition, we present a new method to characterize the instrument detection efficiency as a function of particle size that relies on measuring the mobility and vacuum aerodynamic size distributions of polydisperse spherical particles of known density. We show that a new aerodynamic lens used in SPLAT II improves instrument performance, making it possible to detect 83 nm particles with 50% efficiency.     

Effect of Acoustic Radiation on DMA Resolution

Acoustic waves produced by pressure fluctuations in the turbulent exhaust region of differential mobility analyzers (DMAs) are radiated upstream, making the flow in the working region slightly unsteady and reducing DMA resolution. This claim is demonstrated in a variety of settings. First, a resonance has been observed in several DMAs where the resolution decreases drastically in a narrow range of flow rates. This resonance can only be acoustic, and must be excited by flow unsteadiness, which is only present downstream. Second, non-idealities observed in two very different DMAs are suppressed when they are operated under transonic conditions. This is consistent with the inability of acoustic waves to propagate upstream against a supersonic flow. Third, these non-idealities decrease when the turbulent exhaust region from which acoustic radiation would originate is not in direct sight with the DMA's working section. These findings suggest new strategies to achieve DMA resolving powers approaching 100 under subsonic conditions.     

Modelling the Effect of Particle Size in Microfiltration

Abstract

Particle deposition at the filter surface in microfiltration is studied to better understand the effect of particle size on cake morphology and permeability reduction. Numerical simulations are carried out on a Hele Shaw cell which consists of a representative unit element of a two dimensional spatially periodic flat plate with pores. The particle concentration in the fluid is assumed to be low so that particles enter one by one into the computation domain. Particles follow the flow streamlines under creeping flow conditions from a random initial location until they are subjected to physico‐chemical interactions near the filter surface or a particle already deposited. The computational domain consists of two regions: a fluid region and a porous medium region, i.e. the particle cake. The flow over the two regions of the Hele Shaw cell is computed using the Darcy model, including the variations of the permeability field due to the cake formation. Results show that both the permeability and the filtration efficiency are affected significantly by particle size.     

动态力学分析仪在轮胎胎面胶料性能分析中的应用

采用动态力学分析仪（DMA）对不同硫化条件下的胎面胶料进行了动态性能测试分析,采用不同受力方式对不同胎面胶料进行了动态性能分析。这些分析表明,DMA在硫化后胶料性能的研究方面发挥了很大的作用,为胶料配方的设计发挥了很好的指导作用。     

Effect of Particle Shape on Inline Particle Size Measurement Techniques

The influence of the particle shape on the results of different measuring techniques was investigated. Considered were single‐frequency ultrasound technique, 3D optical reflectance measurement (advanced particle analyzing system with multi capture signal technology), and focused‐beam reflectance measurement probes as techniques which are usable inline and in suspension density ranges usually present in industrial crystallization processes. Advantages and shortcomings of these techniques are compared and discussed.     

The Scan Time Effect on the Particle Size Distribution Measurement in the Scanning Mobility Particle Sizer System

The scan time effect in the scanning mobility particle sizer was confirmed. The magnitude of this effect was shown in a typical situation. The cause of this scan time effect is the mixing process described by Russell et al. (1995). In that case, the result obtained at the longer scan time is the more accurate one.     

On the Reversible Nature of Rubber Particle Cavitation in Toughened Thermoplastics

Toughening of brittle thermoplastics by addition of a separated rubber phase has been an important area of research in industrial material development. Several research groups have focused their efforts to understand the role of the dispersed rubber particles for toughening of plastics. As a result of the research work, the debonding of grafted rubber particles from the surrounding rigid matrix and as well the internal rupture of particles, i.e., cavitations, were considered as a possible dominating contribution of particles to toughening. Recently a method for the detection of rubber cavitation in rubber toughened thermoplastics, based on the observation of the rubber cavitation phenomena occurring during a cooling procedure and detected by means of thermal contraction measurements, has been developed by Dijkstra and co‐workers. During such experiments an S‐shaped deviation from linear thermal contraction has been observed. This behavior was attributed to the cavitation of rubber particles under thermally induced hydrostatic tensions during cooling. The present paper is aimed at showing that the observed S‐shaped deviation from linear thermal contraction during cooling reoccurs during subsequent cooling steps if an appropriate thermal loading of the samples takes place after the first cooling. This result provides an even stronger evidence that the S‐shaped deviation from linear thermal contraction during cooling is indeed caused by particle cavitation. It is also shown that the cavitation behavior of rubber particles in toughened thermoplastics depends strongly on thermal history, rubber phase volume of the sample under investigation and experimental conditions as well. Based on these results the method has to be used very carefully for a general quantitative comparison of different rubber modifiers in toughened plastics. However, such contraction tests can be considered as an additional tool to understand basic deformation behavior of rubber modified thermoplastics.     

搅拌速度和颗粒尺寸对复合电沉积Ni-cBN复合量的影响及机理分析

决定金属-陶瓷复合耐磨镀层摩擦学性能最为关键的因素是硬质强化颗粒的尺寸和含量。通过分别选用两种粒径的cBN颗粒,在氨基磺酸镀镍液中电沉积Ni-cBN复合镀层,研究搅拌速度和颗粒粒径对复合量的影响规律,并对其影响机理进行分析。研究结果显示,随搅拌速度的增加,两种粒径的cBN颗粒的复合量均呈现先升高后降低的趋势,且在搅拌速度偏高时,较大粒径cBN颗粒的复合量的下降趋势更加明显。从搅拌速度、颗粒粒径、复合量三者之间的关系分析,颗粒与电沉积金属层之间不是单纯依靠机械结合,两者之间应该存在一定的界面作用力,使得在镀层厚度与颗粒粒径之比很小时,颗粒就能被镀层捕获。     

Technical Note: A New Deconvolution Scheme for the Retrieval of True DMA Transfer Function from Tandem DMA Data

Experiments were conducted to determine particle removal efficiencies from surfaces due to air jet impingement. We utilize monodisperse fluorescent polymer spheres ranging from 1 μm to 45 μm diameter distributed on polycarbonate surfaces and muslin cloth. Particle removal efficiencies are determined from cloth that simulates clothing or fabrics, surfaces important for trace explosives detection. Optical images of the sample surface are taken using a fluorescence microscope (488 nm radiation) before and after being challenged by a pulsed air or nitrogen jet. The jet is oriented at 45 degrees with respect to the particle laden substrate and is precisely aligned onto the center of the optical axis of the microscope. Particle removal rates are determined by automated particle counting implemented by image processing and analysis. We found that the cloth surface has a release rate comparable to the rate for polycarbonate surface under similar jet conditions. As expected, there is a particle size dependence on removal efficiency, with larger particles being more easily removed.     

Analysis of Scanning DMA Transfer Functions

A new approach to determine transfer functions of scanning differential mobility analyzers (DMAs) is introduced. An expression for non-diffusive particle trajectories in a cylindrical DMA operating in a scanning voltage mode is obtained analytically. Particle trajectory simulations are then used to determine the scanning DMA transfer functions. The results suggest that the shape of the scanning DMA transfer functions may vary with mobility for scan times smaller than a certain value, which depends on the DMA flowrates, and this provides one criteria limiting the fastest scan possible with the conventional DMAs. A simple approach to determine upscan scanning DMA transfer functions in near real-time with minimal number of simulations is described. For upscan operation, the choice of the scantime is seen to impose upper and lower limits on the particle mobility range classified by a scanning DMA. The predicted effect of voltage scanning on altering DMA transfer functions is validated with fast scan experiments.     

粒子群优化算法的研究

粒子群优化算法是一种基于群体智能的优化算法。介绍粒子群优化算法及其基本原理,给出各种改进技术及研究现状,并展望未来的发展趋势。     

Effect of N,N-dimethylacrylamide (DMA) on the comprehensive properties of acrylic latex pressure sensitive adhesives

Acrylic pressure sensitive adhesive (PSA) latexes were synthesized via a monomer-starved seeded semi-continuous emulsion polymerization process with butyl acrylate (BA), methyl methacrylate (MMA), N,N-dimethylacrylamide (DMA), acrylic acid (AA) and 2-hydroxyethyl acrylate (HEA) as monomers. Impacts of DMA on the resultant latex and PSA properties were comprehensively investigated. Results indicated that latex particle size was independent of the amount of DMA in the pre-emulsion feed with excessive and constant surfactant concentration. Latex viscosity increased with DMA concentration. It was also found that water resistance of acrylic latex PSA became worse by the presence of DMA, confirmed by water contact angle measurements. Besides, DSC results showed that as the amount of DMA increased, glass transition temperatures (T_g) of the polymers were elevated significantly. TGA results showed that thermal stability of PSA was improved with DMA as a co-monomer. Furthermore, as DMA amount increased, gel content slightly increased, while sol molecular weight (M_w, M_n) of the polymer decreased. Finally, with respect to the adhesive properties of the PSA, it was observed that loop tack initially increased and then decreased with the addition of DMA from 0 to 4 wt%, and the maximum value appeared at 1 wt%. Peel strength reduced, while shear strength improved with increased DMA concentration.     

粒径对褐煤煤粉流动性影响研究

为了给工业制备流动性好的煤粉提供技术支撑,采用工业分析仪、扫描电子显微镜和超声衰减粒度仪对6种不同粒径的褐煤进行了分析,并采用流动性指数法研究了粒径对煤粉流动性的影响规律,分析表明6种不同粒径褐煤的工业分析组分相近,褐煤颗粒表面粗糙、结构疏松且具有丰富的孔隙结构.研究发现采用休止角、平板角、压缩度或流动性指数获得褐煤煤粉流动性的结论存在差异,流动性指数法用于评判煤粉流动性具有较高的可靠性.流动性指数法表明124～1000μm的煤粉流动性良好,74～124μm的褐煤流动性相当良好,45～74μm的褐煤流动性一般,小于45μm的褐煤流动性不大好,褐煤的流动性随粒径减小而变差.     

Effect of Particle Size Distribution on the Sintering of Alumina

The effect of particle size distribution on the sintering of Al₂O₃ was investigated. Samples could be sintered to high relative density (∼99%), small average grain size (1 μm), and no growth of exaggerated grains using powders with either broad or narrow particle size distribution. However, the broad particle size distribution provided the advantage that powder compacts could be prepared with higher green density and, therefore, samples could be densified with less total shrinkage.     

橡胶粒子对HIPS性能的影响

低顺式橡胶乙烯基含量高,合成的HIPS橡胶相体积分数较大,所含的胶粒较大,产品柔韧性、耐热性能较好;高顺式橡胶乙烯基含量较低,合成的HIPS橡胶相体积分数较小,所含的胶粒较小,产品抗冲击性能较好。使用适当比例掺合的增韧胶,可以获得综合性能良好的HIPS。相关的工艺条件对HIPS性能有一定影响。     

Eliminating the main source of instability and turbulence in TSI's 3071 DMA

The transfer function of TSI's widely used 3071 Differential Mobility Analyzer (DMA) widens drastically when the flow rate Q of sheath gas exceeds 30–40 lit/min, limiting its ability to resolve very small particles. This flow instability is unexpected at the prevailing relatively small Reynolds number (Re < 400). Here, we note that the rings holding the laminarization screens penetrate into the flow channel, generating unsteady vortices. A screen step exists not only on the outer screen region, but also on the inner screen region. Using a new step-free screen, no critical transition is observed up to the highest flow rate achieved of Q = 103 lit/min. The original DMA widens the flow cross-section in the mixing region where the aerosol joins the sheath gas. The flow deceleration then arising at small aerosol input flow rates introduces another source of transfer function broadening, which, however, has negative resolution effects only at Q > 60 lit/min. This feature is suppressed here by modifying a single inlet piece. Although the two flow improvements implemented increase the resolving power in the analysis of very small particles, a substantial non-ideality of unclear origin remains: the best resolving power R found with electrosprayed ions of the protein Immunoglobulin is R = 13.9 for the trimer (IgG)₃, and 12 for the monomer, even at a sheath/aerosol flow ratio of 100.

© 2017 American Association for Aerosol Research     

The Electro-Optical Effect of LC Cells by the Processing Parameter of PI Alignment Layer

The electro-optic characteristics of Liquid Crystal Displays (LCDs) are deeply affected by those parameters including the kinds of liquid crystals and alignment layer materials, the forming conditions of alignment layer, the substrates alignment mode and the processing conditions of rubbing alignment in the interface treatment. In this study, differential scanning calorimeter (DSC), thermal gravity analysis (TGA) and moisture analyzer are utilized to examine the properties of liquid crystals and PI alignment layer materials. The interface treatment between liquid crystals and PI alignment layers were executed via the alignment technology of unidirectional mechanical rubbing with a rayon velvet cloth. Those LC cell specimens were fabricated using Merck MJ99159 N_P liquid crystal and PI alignment layer material (JSR-AL 21000) with various process conditions. Under those parameters influence of curing, rubbing and alignment direction, cell specimens display various electric-optical effects.     

On the Mechanisms of Colloidal Particle and Vapor Bubble Aggregation in Liquid Flows

Mechanisms of aggregation of micrometrically scaled colloidal particles and vapor bubbles are discussed. It is shown that when particles move in reference to the liquid, the attractive force induced by the flow may be greater than the capillary interaction. Such a situation is realized when capillary interaction is gravity driven, and particles float. For partial (weak) wetting situations, flow-induced and capillary attractive forces may be comparable. If the wetting is good, it will play a decisive role in the realistically achievable values of the flow velocities. Hydrody-namic interaction between particles may be of primary importance for sedimentation and fast dip-coating-induced aggregation.     

Effect of Metal Particle Morphology on the Combustion of Refractory Metals in Nitrogen

The synthesis of niobium nitride by combustion of niobium metal powder under nitrogen atmosphere was investigated. Ignition and propagation characteristics were studied in the region of nitrogen pressure between 5 and 100 atmospheres and solid-phase dilution up to 30 wt%. Within this region of operating parameters, the combustion reaction proceeds without any significant liquid-phase formation, thus exhibiting many features common with the combustion of tantalum in nitrogen. However, the effect of metal particle size on the combustion characteristics was different for the two metal systems. This was attributed to the difference in morphology and microstructure between the niobium and tantalum reactant particles. The operating parameters for efficient synthesis of nearly stoichiometric cubic NbN were determined. Results from appropriately designed experiments under conditions where the filtration limitations were minimized were used to extract the apparent activation energy of the combustion nitridation process, which was found to be 40 809 cal/mol.